UniqueID S032057
Subject S
Grade 8
M S B l o c k S09
MSBlockSeq 07
TIMSS 2003
Content Domain
Chemistry
Main Topic
Acids and bases
Cognitive Domain
Conceptual Understanding
Key
See scoring guide
TIMSS 2003 Released Items: Eighth Grade Science
UniqueID S032057
Subject S
Grade 8
M S B l o c k S09
MSBlockSeq 07
TIMSS 2003
Content Domain
Chemistry
Main Topic
Acids and bases
Cognitive Domain
Conceptual Understanding
Key
See scoring guide
TIMSS 2003 Released Items: Eighth Grade Science
UniqueID
Note:
Code
S032057
Subject S
Grade 8
MSBlock S09
MSBlockSeq 07
To receive credit, responses must refer to neutralization or a chemical reaction that results in products
that do not react with litmus paper. Priority is given to Code 10 then 11. If the neutralization reaction is
mentioned, then Code 10 or 11 should be given even if other correct codes apply. In responses where
chemical reaction is not mentioned, the use of the term neutralization (or a technical equivalent) is
required. Responses that refer ONLY to the acid/base being opposites or canceling each other when
mixed, etc., are scored as incorrect (Code 70).
Response
Item: S032057
Correct Response
10
Explanation refers explicitly to the formation of water (and salt) from the neutralization reaction.
Examples: Hydrochloric acid and sodium hydroxide will mix together to form water and salt, which is
neutral.
The hydrogen ions combine with the hydroxide ions to form water, so the litmus paper does
not change colour.
Note: Responses may use words or a chemical equation. The equation does not need to be completely
correct for credit as long as neutralization is clear.
11
Explanation refers explicitly to neutralization (or equivalent), but the specific reaction is not mentioned.
Examples: When you mix acid and alkali, the mixture becomes neutral and has a pH of 7.
The HCl neutralizes the NaOH, and the NaOH neutralizes the HCl.
The mixed solution is neutral, so litmus paper does not react.
Acid + base = neutral solution
There is a neutralization reaction.
12
Explanation refers to a chemical reaction taking place (implicitly or explicitly) to form products that do
not react with litmus paper (or similar). [Neutralization is not explicitly mentioned.]
Examples: The acid and base react, and the new chemicals do not react with litmus paper.
The chemicals that change the litmus paper must have a chemical reaction to each other.
Therefore they will not change the color of the paper anymore.
They form a new solution that has different properties and doesn’t react with litmus.
19
Other correct
Incorrect Response
70
Mentions only that acid and base are “balanced”, “opposites”, “cancel each other”, or similar.
Examples: The acid and base are opposites and counteract so they cancel each other out.
The acid tries to turn it red and the base just turns it blue again at the same time.
Because they’re balanced out and equal.
79
Other incorrect (including crossed out/erased, stray marks, illegible, or off task)
Nonresponse
99
Blank
TIMSS 2003 Released Items: Eighth Grade Science